Correct me if I'm wrong:

I cannot use Travel Bank funds AND an ETC to purchase a ticket?

If that's correct, then a potential workaround is to book something with the Travel Bank, wait over 24 hours, cancel it, and it'll come in the form of an FFC, and that can be combined with an ETC?

.....

So looks like you still cannot combine an FFC with an ETC. Sounds like you may be able to "convert" an ETC to an FFC by booking and waiting 24 hours and then cancelling. Then I'd have multiple FFC to use.